The present invention relates in general to a magnetoresistive head that reads information from a magnetic recording medium using a magnetoresistive effect and a fabricating method thereof, and a read write separation type head that combines a magnetoresistive head with a magnetic recording head. More particularly, the present invention relates to a magnetoresistive head capable of read/write operations at high recording densities.
A magnetic head used in a hard disk drive (HDD) includes a write head and a read head. The write head records information in the form of a magnetization signal on a magnetic disk (a recording medium). The read head reads information recorded in the form of the magnetization signal on the recording medium. An electric signal is translated to corresponding magnetization information and recorded by the write head. The recorded magnetization information is converted to a corresponding electric signal and read by the read head. A late development of the read head is a magnetoresistive head that makes use of a magnetoresistive effect to read the magnetization information. The magnetoresistive head is capable of reading magnetization information recorded as much weaker and feebler signals, contributing to an improved recording density.
The magnetoresistive head includes a sensing region, or a magnetoresistive sheet unit. The magnetoresistive sheet unit includes a pinned layer, a nonmagnetic layer, and a free layer. The pinned layer has a fixed magnetization direction. The nonmagnetic layer is formed in contact with the pinned layer. The free layer is formed in contact with the nonmagnetic layer. Further, a magnetic domain control layer and an electrode film are disposed on an end portion of the magnetoresistive sheet unit. The magnetic domain control layer controls the magnetization direction of the free layer. The electrode film lets current flow through the magnetoresistive sheet unit. In addition, ferromagnetic shield films are disposed on an upper portion and a lower portion, respectively, of the magnetoresistive sheet unit. The free layer changes the magnetization direction thereof according to the magnetization direction of the magnetization information recorded on the recording medium. When the magnetization direction of the free layer changes, a difference produced from the changed magnetization direction of the free layer and the magnetization direction of the pinned layer varies a resistance of the magnetoresistive sheet unit. The hard disk drive is constructed so as to read this change in resistance by translating the change to a corresponding electric signal.
It is necessary to make current flow in order to read the change in resistance of the magnetoresistive sheet unit. The electrode film disposed on the end portion of the magnetoresistive sheet unit accomplishes this task of allowing the current to flow through the magnetoresistive sheet unit. The magnetization direction of the free layer is arranged so as to sensitively respond to and vary with a weak recording magnetic field of the information recorded on the recording medium. It is, on the other hand, required that good reproducibility and stability be assured of a state of magnetization reached as a result of a change caused by a magnetic flux of medium recorded magnetization from an initial state of magnetization. To that end, the free layer is assigned with a uniaxial anisotropic characteristic of magnetization. Further, the magnetic domain control layer formed by a ferromagnetic film is disposed on an end portion of the free layer, whereby a magnetic field is applied thereto.
The magnetoresistive sheet unit is disposed within the upper and lower magnetic shield films. This is done to ensure that the unit responds only to the weak recording magnetic field recorded on the recording medium without being affected by any other external magnetic fields. It is also done so that the medium recording magnetic field can be efficiently induced to the free layer of the magnetoresistive sheet unit. The magnetoresistive sheet unit, and the magnetic domain control layer and the electrode film disposed on the end portions thereof, must be electrically insulated from the magnetic shield films disposed on the upper and lower portions thereof. The magnetoresistive sheet unit therefore includes electrical insulators interposed between these layers.
The magnetoresistive head is fabricated as below. Specifically, a required film is formed on a substrate. A photoresist having a specified pattern is formed on the film. The film is then etched with the photoresist pattern. The photoresist is thereafter peeled off to form a film shape. These steps are repeated to form a magnetic head structure. Different film forming techniques are used according to the characteristics of the film involved. Specifically, an electroplating technique is used for the magnetic shield film. A sputtering or an ion beam sputter technique is employed for forming the magnetoresistive sheet unit films. An RF sputtering technique may be used for forming an Al2O3 film as an insulating film. For the photoresist, an appropriate type of organic photosensitive material is selected and applied and a mask shape is formed using a short-wavelength stepper. Some later stepper models use electrons as well as KrF and ArF.
The fabricating sequence of steps may be classified, in many cases, into the following processes. The processes, specifically, include: a process for forming the lower magnetic shield film; a process for forming films for the magnetoresistive sheet unit; a process for forming a track width of the magnetoresistive sheet unit and forming the magnetic domain control layer and the electrode film on both ends thereof; and a process for forming the upper magnetic shield film.
To increase magnetic recording density of a magnetic recording device, it is necessary to make the magnetization information written in the magnetic recording medium as narrow in width and short in length as possible. It is also necessary to ensure that the magnetization information, thus made narrower and shorter, is read with no errors involved. What happens in the magnetic recording device arranged to offer a high recording density capacity, therefore, is a trend toward a shorter magnetization transition length attempted to achieve by increasing as much as possible a recording frequency in a direction of a write head's writing the magnetization information. Another trend in the magnetic recording device offering a high recording density capacity is toward a narrower writing width (a magnetization track width) of the write head. Generally speaking, the magnetization information that is made smaller features a smaller magnetization amount per unit block of information, a smaller read output, a reduced read efficiency, increased noise, and hence an increased read error rate.
A number of studies are actively carried out on the pinned layer and the free layer with the aim of improving characteristics of the magnetoresistive sheet unit. The pinned layer is typically a laminated structure of an antiferromagnetic film and a ferromagnetic film. To improve the characteristics of the pinned layer, however, studies are under way on antiferromagnetic film materials and ways of making a laminated structure of the ferromagnetic film. Studies are also being conducted on the free layer to examine ways of making a multilayered structure of a synthetic ferrimagnetic type and of oxidizing a multilayered film interface.
The magnetic domain control layer for controlling the magnetization direction by applying a bias magnetic field to the free layer has the following problem. Specifically, if the bias magnetic field is increased, a reduced signal output results with a gain in stability in the signal output. This makes it necessary to optimize the bias magnetic field in response to the magnetic track width or the structure of the magnetoresistive sheet unit. An attempt has therefore been made to solve this problem as disclosed, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-119534) (see FIG. 3). The attempt is to localize and minimize the bias magnetic field from the magnetic domain control layer by correctly aligning the height of the free layer with that of the magnetic domain control layer. According to the approach as disclosed in Patent Document 1, the use of a hard magnetic film having a high coercivity for the magnetic domain control layer ensures good stability while maintaining a high signal output. Another attempt that has been made is to control the magnetization direction of the free layer by laminating an antiferromagnetic film on the free layer, or to dispose a laminated soft film, instead of using the hard magnetic film for the magnetic domain control layer.
To meet the requirement for keeping resistance of the electrode film as low as possible, studies are under way of using a low resistance material for forming the electrode film. Typical materials for the electrode film include low resistance materials of Au, Rh, and the like, and high fusion point materials such as Ta, Cr, and the like, and alloys thereof.